1. Field of the Invention
The invention consists of a significantly improved long lasting thermoformable phosphorescent acrylic resin blend, filled or unfilled, for casting, molding, coatings, liquid inlays and adhesives. Specifically, the present invention relates to the thermoformable, photoluminescent, thermoluminescent and electroluminescent properties. These polymer composites are characterized by unique, long lasting glow-in-the-dark properties exhibited after being exposed to light. The visual afterglow lasts for 10 hours or more after proper exposure to light.
2. Description of the Background
Products of the general character of acrylic resins as mentioned above are commercially available under many trade names such as Corian, LG Hi-Macs, Lucite, Staron, Formica, etc. Acrylic resin materials have long been known and commonly available for use as kitchen and bathroom surfaces, cubicle dividers and wainscoting, etc. Broadly speaking these materials are formed from thermoset acrylic and or unsaturated polyester resins. Fillers range widely and are used to improve thermal and mechanical properties, impart rigidity, flame retardance and are used to give particular visual effects to the product. Many prior existing patents are directed to these types of products. Examples of those patents include “Filled Polymethylmethacrylate Article and Process for its Manufacture” in Duggins et al. U.S. Pat. No. 3,827,933; “Thick Cured Polymethylmethacrylate Article and Process for its Preparation” in Slocum U.S. Pat. No. RE. 27,093: “Use of Alumina Trihydrate in a Polymethylmethacrylate Article” in Duggins U.S. Pat. No. 3,847,865, these being but a few of the many U.S. patents that exist in this field.
The aforementioned products have experienced tremendous commercial success as surfacing especially for countertops and tabletops in kitchen and bathroom surfaces as well as vertical applications like wall cladding and signage. The said products (broadly termed as Solid Surface), are non-porous, solid materials that are manufactured in a variety of colors and patterns that run throughout the product yielding a soft, translucent warm look. This material is repairable, thermoformable, resistant to heat, impact, fungal and bacterial growth. The material can be easily repaired when damaged (breaks or cracks) and renewed (normal wear, staining, etc.) to its original look:
Pigments commonly used in these products are composed of small particles of inorganic compounds, generally metallic oxides that are approximately spherical in shape. Other pigments, fillers and aggregates (larger pieces of colored material) are used to produce various visual effects. Alumina Trihydrate (ATH) is commonly used filler due to its particular fire retardant properties.
Luminescence has been a long observed natural phenomenon. Heat has long been known to excite and cause liquids and solids to emit shorter wavelengths of light as their temperature increases. Examples of this would be a metal that is increasingly heated proceeding through a red glow until becoming ‘white hot’. This phenomenon is commonly referred to as incandescence or a light produced by heat. Incandescence has been a useful method of producing light for many years and includes fire, candles, various types of oil and gas lamps and electrically stimulated bulbs using tungsten as a filament. Electrical current has been well known to cause certain gases like neon to become luminescent.
In contrast there is also a phenomenon of fluorescence/phosphorescence that does not require the application of heat. Fluorescence differs from phosphorescence only in the duration of the afterglow. Fluorescence afterglow is measured in seconds, while phosphorescence is measured in minutes/hours. Examples of naturally occurring ‘cold luminescence’ (hence termed phosphorescence) include organisms that exhibit bioluminescence, examples of which are foxfire (a fungus-growing on decaying material that produces light), lightning bugs, glow worms and various deep sea denizens. Certain naturally occurring chemicals like phosphorous exhibit a dim glow Other compounds like phosphors for example, are luminescent (phosphorescent) after exposure to sunlight, x-rays or electron beams.
There are many phosphorescent substances including sulfides, silicates, metal aluminum oxides, silicates and rare earth oxides. Zinc sulfides are the most well known phosphorescent pigment. Zinc sulfide can be activated by adding various activators, the most common of which is copper (forming ZnS:Cu). Aluminum, gold, gallium, manganese, indium, scandium, lead, cerium, terbium, europium; gadolinium, samarium, praseodymium or other rare earths and halogens can all be used to activate the zinc sulfide by incorporating into the crystal lattice structure. Other sulfide phosphors include ZnCdS:Cu, ZnCdS:Ag, CaS:Bi, CaSrS:Bi alpha barium zinc sulfides, barium zinc cadmium sulfides, strontium sulfides and others. Various patents describe the use of the aforementioned substances. For example, U.S. Pat. No. 3,595,804 (1971) to Martin, Jr. discusses the method used to improve the zinc sulfide and zinc cadmium sulfide phosphors having aluminum and being activated with silver or copper. U.S. Pat. No. 5,558,817 (1996) to Bredol, et al. explains the method of manufacturing luminescent zinc sulfide activated by copper and aluminum. U.S. Pat. No. 3,970,582 (1976) to Fan, et al. deals with luminescent materials comprising alpha barium zinc sulfides or barium zinc cadmium sulfides activated with cerium, europium, lead, manganese or terbium and their method of manufacture. U.S. Pat. No. 3,957,678 (1976) to Dikhoff, et al. also deals with a method of manufacturing zinc sulfide and or cadmium phosphors.
Aside from the previous patents mentioned, describing the manufacture of the pigments themselves, there are many patents to describe zinc sulfide type phosphorescent pigments and their use specifically in thermoplastic and thermoset applications. Some examples are: U.S. Pat. No. 4,211,813 (1980) to Gravisse, et al. (Photoluminescent textiles using metal sulfides), U.S. Pat. No. 5,692,895 (1997) to Farzine-Nia, et al. (Photoluminescent orthodontic appliances using zinc sulfide with calcium cadmium and strontium), U.S. Pat. No. 5,605,734 (1997) to Yeh, et al. (Phosphorescence carpets with directional signs using copper or zinc sulfide doped with copper and manganese), U.S. Pat. No. 5,674,437 (1997) to Geisel (luminescent fibrous material using metal aluminate oxide pigments with a thermoplastic polymer. The luminescent comprised as a thermoplastic polymer such as polypropylene, polyamides, polyesters, polymethacrylics, polyacrylates, polycarbonates, PVC, polyethylene, acrylic resins, polyurethane, halogenated polymers, etc. U.S. Pat. No. 5,607,621, (1977) to Ishihara, et al. covers making phosphorescent resins and formed articles using zinc sulfide doped with copper and resinous materials such as ABS resins, acrylic, acetals, PET, nylon, PVC, etc.
However, all zinc sulfide derivatives suffer from the problems of being degraded by UV light in the presence of moisture and especially from a relatively short afterglow. These limitations negate the use of zinc sulfide combinations by themselves in any phosphorescent product that requires long lasting afterglow or are exposed to any UV light source.